Filariasis

What is Filariasis?

Filariasis is a disease that is caused by infection with a parasitic worm (filarial nematodes). The disease is spread by blood-sucking insects, primarily mosquitoes.

The insects ingest the filariasis larvae (microfilariae) while feeding on blood from infected people, then transmit them by biting others. Once deposited on the skin or in the blood stream of a new host, the worms mature and live in or near lymphatic vessels and lymph nodes. The mature worms reproduce large numbers of immature worms that may be found in the blood.

The body's defense (immunologic) reaction to the worms causes damage to lymphatic tissues and accounts for many of the disease symptoms. Early acute disease may be without symptoms and inconspicuous (occult). It may become a chronic disease obstructing lymph and lung function.

The disease is common in tropical and subtropical regions of the world such as tropical Africa, Indonesia, the Southern Pacific Rim, southern Arabia, southern Mexico, and Guatemala.

History: The history will include travel in tropical or subtropical areas and significant history of insect bites. The incubation period will have been at least eight months for travelers and up to two to three years for native persons in a country where filariasis is prevalent. Symptoms of acute disease include episodes of fever with pain and/or swelling of lymph nodes (lymphadenitis) and lymphatic vessels (lymphangitis). These episodes will occur at irregular intervals and last several days.

With disease progression, inflammation of the epididymis or testicles as well as involvement of the abdominal, pelvic, and peritoneal lymph vessels may occur intermittently. Lymph node enlargement may persist. Allergy-like symptoms of hives and rashes are likely to be found in travelers who are infected repeatedly.

Individuals with chronic disease may show symptoms of obstruction and interference with normal lymphatic flow. Symptoms may include a rapid increase in the size (mass) of the extremities, genitals, or breasts. Episodic nighttime coughing or wheezing may be reported.

Physical exam may show characteristic painful/swollen lymph nodes (lymphadenitis), which is most severe at the affected node and decreases in intensity with distance from the node (retrograde). In later stages, involvement of the peritoneal lymphatics will also occur in a retrograde fashion.

Abdominal palpation (examination by pressing on the abdomen) may reveal a swollen spleen or liver.In chronic cases, swelling of the scrotum and enlarged lymphatic vessels are characteristic physical symptoms. The infected area, commonly a limb or the scrotum, becomes enormously enlarged, and the skin becomes thick, coarse, and cracked (fissured).

Hard masses may accumulate in the breasts, legs, hands or testicles. A milky, white substance (chyle) may appear in the urine as a result of lymphatic vessel rupture into the urinary tract.

Tests: The diagnosis of filariasis is confirmed by microscopic examination of blood or lymph fluid for the presence of microfilariae.

Blood tests will show immature worms in the blood after six to twelve months of infection. It may take two to three years for worms to develop in the blood of indigenous persons. Worms may also be present in fluids drawn from swollen areas. Each species of filarial nematode will show characteristic structure and form (morphology) under microscopic examination. Microscopic (histologic) examination of the skin in areas of mass accumulation will show hardening and loss of elasticity. Lymph nodes may become fibrotic and secondary bacterial infections may be detected.

In blood studies (serology), chronic infections may show high filarial antibody titer and IgE levels. Lung infection will show high eosinophil counts (eosinophilia). In occult disease, worms are not present in the blood. Adult worms may be detected in tissues using ultrasonography. X-rays may show scattered, small nodular lesions on the lungs. There may be increased evidence of vascular damage on the chest films.

Filariasis may be treated in early, mild cases with a three-week course of antifilarial drugs. This medication usually cures the infection, but may cause a reaction marked by fever, illness, and muscle or joint pains. Treatment for symptomatic relief includes bed rest, antibiotic use for secondary infections, elastic stockings and pressure bandages to reduce swelling and fluid accumulation, and suspensory bandaging for swollen testicles or breasts. Chronic infections are more difficult to treat effectively. Small accumulations of fluid may benefit from local injection of sclerosing (condensing) agents. Surgery may be required. Mass accumulations may be managed using shunt procedures combined with removal of excess fatty and fibrous tissue, drainage and physical therapy.